Method and apparatus employing two stage refrigerant for solidifying a gaseous component



May 7, 1968 M. w. GARLAND 3,381,486

STAGE REFRIGERANT Filed Sept. 29, 1965 Qm EmoEhmm 50560 FOR SOLIDIFYING A GASEOUS COMPONENT METHOD AND APPARATUS EMPLOYING TWO 09 lllllllll III! III INVENTOR MILTON W GARLAND ATTORNEY United States Patent 3,381,486 METHOD AND APPARATUS EMPLOYING TWO STAGE REFRIGERANT FOR SOLIDIFYING A GASEOUS COMPONENT Milton W. Garland, Waynesboro, Pa., assignor to Frick Company, Waynesboro, Pa., a corporation of Pennsylvania Filed Sept. 29, 1965, Ser. No. 491,149 6 Claims. (Cl. 62-12) ABSTRACT OF THE DISCLOSURE A system for the separation of constituents of a mixture of fluids by causing at least one of the constituents to solidify upon the lowering of the temperature of the mixture, the system comprising a plural stage refrigeration system, each of which stages have compressor means for producing refrigerant fluid at different temperaturepressure Values and a first and second plurality of heat exchangers. Each of the first and second plurality of heat exchangers is connected together for series flow of the mixture of fluids and with each heat exchanger connected to a different stage so as to receive, in relation to the direction of flow of the fluid mixture, refrigerant fluid at successively lower pressure-temperature values. Valve means is provided for alternating the flow of the fluid mixture between the first and second plurality of heat exchangers. A defrost means is connected to each of the heat exchangers to convert the solidified fluid in the heat exchangers, through which fluid mixture flow has been stopped, to a fluid state to facilitate removal of the fluid from the heat exchangers.

This invention relates to fluid temperature reducing systems and more particularly to an apparatus for and method of separating one fluid suspended in another fluid by reducing the temperature of the fluids sufiiciently to cause the one fluid to solidify and thereby separate from the other fluid.

In the production of oxygen, it is common practice lU provide a refrigerating system for removing the water content of a stream of compressed air by freezing the water and collecting the same. In such systems the refrigerant is passed in indirect heat exchange with the compressed air in a heat exchanger, which is designated an evaporator in a refrigeration system, to lower the temperature of the air below the freezing point of water so that the water accumulates on the heat exchange surfaces in the form of frost and compressed, water-free air is discharged for further processing. As the frost accumulates on the heat transfer surfaces, the efficiency of the heat exchange surfaces is gradually reduced until the heat exchanger does not function to remove, by freezing, the required amount of moisture. At a time prior to a build-up of frost, which would not permit eflective removal of water, the heat exchanger or evaporator must be defrosted. Defrosting of the heat exchange surfaces requires the heating of those surfaces and this is usually accomplished by flowing high pressure, high temperature gaseous refrigerant through the heat exchanger elements. After defrosting, the flow of compressed air is again directed through the heat exchanger.

The disadvantages of the above described system are that the system has to be manually controlled and the sudden return of the relatively hot compressed air flow through the defrosted heat exchanger caused undesirable refrigerant flood back and, until the unit cooled down sufficiently, the outlet temperature of the compressed air was above that desired. The outlet temperature of the 3,381 ,486 Patented May 7, 1968 compressed air might continue to be above the predetermined desired value for as much as an hour.

Accordingly it is one of the objects of the present invention to provide a process and apparatus for removing moisture from a product fluid by freezing the water and collecting the same, which system is continuous and provides a substantially constant product outlet temperature.

Another object of this invention is to provide a process and apparatus for removing moisture from a product fluid by freezing and collecting the water, which system eliminates refrigerant flood back and fluctuations in the temperature of product outlet flow.

A further object of this invention is to provide a relatively simple and non-complex system for removing water from a fluid containing Water by freezing the latter which readily lends itself to automatic control.

A still further object of the present invention is to provide a two-stage refrigeration system for effecting separation of water contained in a product fluid wherein product outlet flow is relatively constant and at a relatively uniform predetermined temperature.

In view of the foregoing the present invention contemplates a system for the separation of the water content of a product fluid by freezing which comprises a two-stage refrigerating system wherein each stage includes a set of heat exchangers or water chillers arranged in parallel to each other and connected so that each set alternately receives series flow of product fluid therethrough. Each heat exchanger is constructed and arranged to pass refrigerating fluid, such as freon or ammonia, in indirect heat exchange relationship with the product fluid to freeze the water out of the product fluid. Each heat exchanger of each set is connected to receive relatively hot, gaseous, refrigerant fluid when it is necessary to defrost the heat exchangers to permit remova of the Water and to restore the efficiency of the heat exchangers.

To provide for continuous flow of product fluid, a valve means is provided to alternately direct product fluid flow through one set of heat exchangers while the other set of heat exchangers is being defrosted.

An accumulator means is disposed in the refrigerating system and is connectedto each set of heat exchangers to provide a reservoir of refrigerating fluid for reducing the temperature of the defrosted set of heat exchangers to the design temperature before restoring flow of product fluid through the defrosted heat exchangers.

A recirculation or bypass line, interconnecting the accumulator means with the high pressure liquid side of the refrigeration system, is provided to achieve a balanced system under a very wide range of flow rates of product fluid (load).

The invention will be more fully understood from the following description when considered .in connection with the accompanying schematic drawing of the system according to this invention.

While the system will be described as applicable to an oxygen production process wherein water must be removed from compressed air, it is to be understood that the invention has much broader application. The system, according to the present invention, may be employed to remove water from a liquid, such as alcohol or other liquid immiscible with water. It, also, may be employed to merely reduce the temperature of a fluid where the removal of water content is desirable or, at least, not objectionable.

Now referring to the drawing the system comprises a two stage refrigeration system 10 cooperatively associated with a fluid product flow system 12 to effect a separation of moisture contained in compressed air flowing through fluid product flow system.

Refrigeration system The two stage refrigeration system comprises a first stage consisting of a primary compressor 14 connected to a condenser 16 by a line 18 to pass relative high temperature, compressed, gaseous refrigerant to the condenser. The condenser 16 is connected to a receiver 20, via a line 22, to pass high pressure, high temperature, liquid refrigerant to the receiver. From receiver 20, the high pressure, liquid refrigerant flows, via line 24, to a heat exchanger 26 and, through the heat exchange elements 28 of the heat exchanger, to a gas-liquid cooler and high temperature accumulator 30, via a line 32. The flow of liquid refrigerant, through lines 24 and 32, is regulated by a solenoid valve 25. Solenoid valve 25 is electrically actuated in response to the liquid level in accumulator 30, which level is sensed by a sensing device 76. In heat exchanger 26 the liquid refrigerant passes in indirect heat exchange relationship with compressed air as will be more fully explained hereinafter. Accumulator 30 has a sump 34 which provides a reservoir for liquid refrigerant. The sump 34 is connected by a line 36 to the inlet of a pump 38 so that liquid refrigerant is pumped from sump 34. The pump 38 discharges liquid refrigerant, via line 48, to lines 42 and 44 which are in communication with a set of primary water chillers or heat exchangers. The set of heat exchangers comprises two heat exchangers 46 and 48 which are connected, respectively, to lines 44 and 42 and are arranged in parallel fiow relation to each other. Flow of liquid refrigerant, through lines 44 and 42, is controlled by solenoid actuated valves 50 and 52 disposed in the respective lines. Each of the heat exchangers 46 and 48 are provided with heat transfer elements 54 to conduct the liquid refrigerant in indirect heat exchange relationship with compressed air so that the temperature of the latter is reduced and at least part of the liquid refrigerant is vaporized. The vaporized or mixture of liquid and vaporized refrigerant flows from the respective heat transfer elements 54 of heat exchangers 46 and 48 to accumulator 30 by way of suction lines 56 and 58. A fluid lift 68 of any suitable type is provided in lines 56 and 58 to provide entrainment of liquid refrigerant in the gaseous refrigerant and prevent slugs of liquid from being discharged into accumulator 30. The vaporized refrigerant fluid is carried from accumulator 30 to compressor 14 by line 62 for recompression by the compressor and recirculation through the first stage of the refrigerating system.

The second stage of the refrigerating system comprises a low temperature-pressure accumulator 64 which is connected by a line 66 to a booster compressor 68 to deliver vaporized refrigerant fluid for compression. The booster is connected to deliver compressed, vaporized refrigerant to accumulator 30, via line 70. Liquid refrigerant is conducted from accumulator 30 to accumulator 64 by a line 72. The flow of liquid refrigerant to accumulator 64 is regulated by a valve 74 which is electrically actuated in accordance with the liquid level in accumulator 64, the liquid level being sensed by liquid level sensing device 77. Accumulator 64 has a sump portion 78 from which liquid refrigerant is pumped by a pump 80, via line 82. From pump 80, liquid refrigerant is discharged, through line 84, to suction lines 86 and 88. Suction lines 86 and 88 communicate with a set of heat exchangers 90 and 92 which are arranged in parallel to each other and in series flow relation to heat exchangers 46 and 48, respectively, With respect to compressed air flow. Flow of refrigerant, through suction lines 86 and 88, is controlled by solenoid actuated valves 87 and 89, respectively. Similar to heat exchangers 46 and 48, heat exchangers 90 and 92 are each provided with heat transfer elements 94 to provide for indirect heat exchange between the liquid refrigerant and the compressed air. The passage of liquid refrigerant in heat exchange relation to the compressed air results in at least partial vaporization of the liquid refrigerant as it absorbs heat from the compressed air. The vaporized or mixture of vaporized and liquid refrigerant is passed from the heat transfer elements 94 to accumulator 64 via lines 98 and 100. Lines 98 and 100 are provided with fluid lifts 96 which are similar to fluid lifts 60 and serve the same purpose. The vaporized refrigerant fluid is returned by line 66 from accumulator 64 to compressor 68 for recompression by the latter.

Product fluid flow system The product fluid flow system 12, as for example, a compressed air flow system, comprises a line 102 which receives air which has been compressed by means, not shown, and which may be at a temperature of 400 Fahrenheit. The compressed air is conducted to a cooling means 184, as for example a heat exchanger which receives cooling water from a cooling tower. The temperature of the compressed air may be reduced in the cooling means to a temperature of F. and is passed from the cooling means, via a line 106, to a three-way valve 108. Three-way valve 108 is adjustable to provide flow of compressed air through either heat exchangers 46 and 90 or heat exchangers 48 and 92 by way of lines 110 and 112. Heat exchangers 46 and 90 are connected together by conduit 114 to provide series flow of compressed air through the heat exchangers. Similarly, heat exchangers 48 and 92 are connected together by a line 116 to provide series flow of compressed air through the heat exchangers. The cooled, arid compressed air is conducted from heat exchangers 90 and 92, through lines 118 and 120, respectively, to a line 122. Line 122 conducts the cooled, arid compressed air into heat exchanger 26 wherein it passes in indirect heat exchange relationship with liquid refrigerant flowing through heat transfer elements 28 of the heat exchanger. Since compressed, arid air discharged from heat exchangers 90 and 92 may be at 80 F., a temperature lower than is necessary for the further treatment of the air, heat recovery is achieved by utilizing heat exchanger 26 to reduce the temperature of the refrigerant fluid. The heated compressed air is discharged from heat exchanger 26, via line 124, to a point for further processing or storage.

Safety by-pass To prevent an undue pressure build-up in lines 42 and/or line 44, a pressure relief valve 126 is disposed in a by-pass line 128 extending between high pressure fluid line 44 and low pressure fluid refrigerant line 56. Similarly, a pressure relief valve 130 is disposed in a by-pass line 132 extending between high pressure line 86 and low pressure line 98, which relief valve 130 is constructed and arranged to prevent a fluid pressure in lines 86 and/ or 88 above a predetermined maximum value.

Balancing circuit To maintain a balanced system under low load or no load condition where flow of compressed air through the product fluid system 12 is reduced or cut off entirely, a balance line 134 is connected at one end to receiver 20 and at the opposite end to accumulator 64. A valve 136 is disposed in balance line 134, the actuation of valve 136 being controlled by a sensing device 140 connected to accumulator 64. The sensing device 140 may either be designed to sense fluid temperature or pressure within accumulator 64 and functions to open valve 136 when the fluid pressure or temperature falls below a predetermined minimum value so that relatively high pressure and temperature, vaporized refrigerant is conducted from receiver 20 to accumulator 64.

Lubricating oil removal Accumulator 30 is provided with a sump extension at 142 below the connection of line 36 with the sump to form a compressor, lubricating oil trap. Lubricating oil which may be entrained in the flow of liquid refrigerant in lines 24 and 32, is separated out of the liquid in accumulator 30 and is trapped in the sump extension 142.

The collected oil is periodically removed from the sump extension by way of a drain line 144. Since high pressure side of compressor 68, as well as the high pressure side of compressor 14, is connected to accumulator there is no need for an oil collecting trap associated with accumulator 64, all refrigerating fluid delivered to accumulator 64 being normally free of entrained lubricating oil. De frosting system Since heat exchangers 46, 48, 9t} and 92 function to remove the water content in the compressed air flowing therethrough by causing the water to freeze and collect on the heat transfer elements 54 and 94 in the form of frost, the heat exchangers must be periodically defrosted. Any suitable means for defrosting the heat exchangers 46, 48, and 92 is within the contemplation of the present invention. One means for defrosting the heat exchangers is shown for illustration purposes and for a better understanding of the invention.

As shown in the drawing, a suitable defrosting system may comprise a line 146, communicating with compressor discharge line 18 downstream of the check valve of compressor 14, to receive hot gaseous refrigerating fluid. The line 146 is connected to branch lines 148 and 150 through a 3-way valve 149. Control of flow, through branch lines 148 and 15% is regulated by a solenoid actuated valve 49. Line 148 communicates with secondary branch lines 154 and 156 which, in turn, communicate with heat exchangers 46 and 90, respectively, by connection with the refrigerant inlet and outlet lines of the heat exchangers. Similarly to line 148, line 150 is connected to two secondary branch lines 158 and 160 which con nect with heat exchangers 48 and 92, respectively, by connection to the refrigerant inlet and outlet lines of the associated heat exchangers. Since the construction and arrangement of the defrost system associated with each of the heat exchangers 46, 90, 48 and 92 is the same, only the construction and function of the piping and components associated with heat exchanger 46 will be described in detail.

As shown, line 154 is connected with the refrigerant inlet line 44 of heat exchanger 46 downstream of valve 50, which valve during the defrost cycle of operation is closed. Line 154 also communicates with a fluid pressure actuated valve 162 through a line 164. The fluid pressure actuated valve 162 is disposed in refrigerant outlet line 56 upstream from fluid lift 60 so that, when high pressure gaseous refrigerant flows into lines 154 and 164, the pressure of the refrigerant fluid actuates valve 162 to a closed position. Simultaneous with the closing of valve 162, hot gaseous refrigerant flows from line 154 into line 44, and thence into heat exchange elements 54 of heat exchanger 46. The gaseous refrigerant, in losing its heat and, thus, melting the frost on the heat transfer elements 54, is liquefied. This liquid is removed and conveyed to the accumulator 30 by a by-pass line which is connected at one end to outlet line 56 of the heat exchanger and to the fluid lift 60 at the opposite end. Intenposed in by-pass line 170 is a pressure regulator valve 171 which is preadjusted to open at a pressure above the freezing point of water, as for example 45 F. To provide defrost with constant control of suction line pressure, a solenoid actuated valve 151 is disposed in line 164 and a bleed down control circuit is provided, which circuit comprises a bleed line 173 connected at one end to line 170 and at the opposite end to suction line 56, the flow through line 173 being controlled by a bleed solenoid valve 175 and a pressure controlled valve 177 communicating with suction line 56 through line 179. A pressure controlled switch 183 is connected to be actuated by fluid pressure in suction line 56 and is electrically connected to solenoid valve 50 to effect actuation of the latter. After a predetermined time interval when all of the frost is melted and the water drained from the heat exchanger through drain line 172, flow of gaseous refrigerant is terminated by the closing 6 of solenoid valves 152 and 151. At this time bleed solenoid valve 175 opens because the defrosted heat transfer elements 54 are at a predetermined elevated pressuretemperature level, as for example 45 F. Since the pressure-temperature valve in suction line 56 must be maintained at its normal, relative low value, as for example -40 F., without any appreciable change, the pressure in heat transfer elements 54 of heat exchanger 46 is slowly reduced by bleeding the high pressure-temperature refrigerant fluid through line 170 and bleed line 173. This bleed down is controlled by pressure actuated valve 177 in response to pressure in suction line 56. If pressure in the suction line reaches a predetermined value above normal system pressure, valve 177 would be actuated to a closed position. Following the bleed-down of fluid pres sure in the heat transfer elements 54 the temperature of the heat exchanger must be reduced to a predetermined low value before flow of product fluid therethrough. Reduction in temperature of heat exchanger 46 is achieved by flowing liquid refrigerant at a controlled rate into heat exchanger 46 by first closing bleed valve 175 and solenoid valve 151. The closing of valve 151 permits valve 162 to open and thereby communicate heat exchanger 46 again with accumulator 30. By opening valve 50, flow of liquid refrigerant is now permitted to flow through the heat exchanger. Since heat transfer elements 54 are warm, a sudden pressure rise would tend to occur, which rise in pressure could seriously effect the normal system operating temperatures, however this is avoided by providing pres sure actuated switch 183 in suction line 56 which is connected to and controls actuation of solenoid valve 50. Any rise in pressure in suction line 56 above a predetermined value will actuate switch 183 to thereby cause solenoid valve 541 to move to a closed position and cease flow of liquid refrigerant into heat transfer elements 54 of heat exchanger 46. When the fluid pressure in suction line 56 returns to the predetermined level, switch 183 is actuated to cause valve 58 to open and permit resumption of flow of liquid refrigerant through heat transfer elements 54 of the heat exchanger. This cycling will continue until the temperature of the heat transfer elements reach the desired normal operating temperature. Thereafter, the heat exchanger is in a condition to receive flow of product fluid therethrough.

Operation In operation of the system for the separation of the water content of a product fluid, as herein described, it will be assumed that 3-way valve 108- is positioned to provide for flow of compressed air through line 110 and, hence, through heat exchangers 46 and 90, and to prevent flow through line 112 and heat exchangers 48 and 92. With compressed air directed through heat exchangers 46 and 90, solenoid valves 50 and 87 are open while solenoid valves 52 and 89 are closed. With compressor 14 operating and solenoid valve 25 in an open position, liquid refrigerant flows from receiver 20, via line 24, into heat exchanger 26. The liquid refrigerant flowing through the heat transfer elements 28 of the heat exchanger is at a relatively high temperature, as for example 90 F. and, in flowing in indirect heat exchange relationship with compressed air which is at a relatively low temperature, as for example 80 F., is cooled and discharged from the heat exchanger at a reduced temperature, as for example 40 F., through line 32. The liquid refrigerant is delivered by line 32 into the high temperature and pressure accumulator 38. From accumulator 30, the liquid refrigerant is pumped by pump 38, via lines 36, 40 and 44, into heat transfer elements 54 of heat exchanger 46. From heat transfer elements 54, the at least partially vaporized refrigerant is returned to the accumulator by Way of line 56. Simultaneously with flow of liquid refrig erant through heat exchanger 46, liquid refrigerant is pumped from low temperature pressure accumulator 64 by pump 80 and, through lines 82, 84 and 86, into the heat transfer elements 94 of heat exc ranger 9d. The liquid refrigerant by passing in indirect heat exchange relationship with compressed air is heated and at least part of the liquid vaporized. The refrigerant fluid is conducted from heat exchanger it? by line 98 to accumulator 64. Vaporizcd refrigerant fluid is conducted from accumulator 30, by way of line 62, to compressor 14 where it is recompressed and passed through condenser 16 and into receiver 28. Vaporized refrigerant fluid in accumulator 64 is conducted by line 66 into the booster compressor 68, and is delivered into accumulator 3% by line '70. Make-up liquid refrigerant is delivered to accumulator 64, from accumulator 30, by line '72 in accordance with the demand as measured by the liquid level in accumulator 64, which level is sensed by the sensing device '77. Similarly, the liquid level in accumulator 30 is maintained Within desired levels by a level sensing device '76 which controls operation of valve 25. For shut-down of the system a valve 266 is provided in line 24. Simultaneously with flow of liquid refrigerant through heat exchangers 46 and 93, as above described, compressed air fiows, from a source thereof (not shown), into a cooling means 104 by way of supply line 162. The cooled, compressed air is discharged from the cooling means 164, via line 195, and into line 116 as directed by 3-way valve 168. As for example, the compressed air may enter the cooling means 364 at a temperature of 400 F. and leave the cooling means at a temperature of 110 F. In cooling the compressed air, it may be placed in a water saturated condition. From line 110, the compressed air passes into heat exchanger 46 and in indirect heat exchange relationship with the liquid refrigerant flow through the heat transfer elements 54 of heat exchanger 46. In passing through heat exchanger 46, the compressed air is cooled and the water content thereof is separated from the air in the form of frost which adheres to the heat transfer elements 54- and the other internal surfaces of the heat exchanger. From heat exchanger 46, the compressed air flows into heat exchanger 90 by way of line 114. In heat exchanger 94 the compressed air passes in indirect heat exchange relationship to the liquid refrigerant flowing through heat transfer elements 94 and is thereby cooled to cause further removal of water in the form of frost which adheres to the heat transfer elements 94- and other internal surfaces of heat exchanger Ell. From heat exchanger 90 the arid, compressed air is conducted into heat exchanger 26 by Way of lines 118 and 122. Upon entering into heat exchanger 26 the compressed air is relatively cold, as for example -8() F. and, in passing in heat exchange relation with liquid refrigerant in heat transfer elements 28 of heat exchanger 26, is heated. The heated, arid compressed air is discharged to a place of storage or to a place of further processing (not shown) through line 124-.

As compressed air continues to flow through heat exchangers 46 and 94}, more and more frost accumulates on the heat transfer elements 54 and 94 of the heat exchangers until the heat transfer efficiency is so reduced that the water content is not as fully removed from the compressed air as is required. Shortly before this incfliciency point is reached the heat exchangers must be de frosted. Defrosting is accomplished in accordance with this invention without interruption of the flow of compressed air and without unbalancing the system.

Befor the defrosting of heat exchangers 46 and 90 is begun, solenoid valves 52 and 89 in lines 42 and 33, respectively, are opened to permit flow of liquid refrigerating fluid through heat transfer elements 54 and 94 of heat exchangers 48 and 92 in the controlled manner as previously described with respect to the defrosting system. This controlled flow of refrigerant continues until the heat exchangers 48 and 92 are brought down to a predetermined design operating temperature at which effective water separation will be achieved upon initial flow of compressed air through the heat exchangers. To

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accomplish this, the accumulators 30 and 6d are of sufficient size to provide the required hold-up of liquid refrigerant to compensate for this added load and by the controlled flow of refrigerant through solenoid valve 50 as controlled by pressure switch 183. The compressor 14 or? must also be selected for capacities which will take into account this added load. After the heat exchanger temperatures have been brought down to the predetermined operational value, compressed air is then permitted to flow through heat exchangers 48 and 92 by actuation of 3-way valve 168 which shuts off flow to and through line 116 and permits flow from line 166 into line 132. As flow of compressed air is permitted through heat exchangers 48 and 92, heat exchangers 46 and 90 are defrosted by the closing of solenoid valve 50, the opening of solenoid valves 153; in line 148, solenoid valve 151 in line 164 and the positioning of 3-way valve 149 to permit flow of high pressure gaseous refrigerant into line 148. The defrosting of heat exchangers 46 and 90 proceeds in the manner previously described with respect to heat exchanger 46. After defrost of heat exchangers 4-6 and 90 has been completed and heat exchangers 48 and 92 approach the condition when they will have to be defrosted, heat exchangers 48 and 92 must be chilled or brought down to a predetermined operative temperature value. This chilling operation is accomplished in a manner to that described for heat exchangers 48 and 92 by opening solenoid valves 50 and 87 in lines 50 and 86, respectively, to permit controlled flow of liquid refrigeraru': therethrough before compressed air is redirected through the heat exchangers 46 and 90.

It is believed now readily apparent that the present invention provides a separation system for removal of the water content of a fluid by freezing the Water which permits continuous flow of fluid to be dehumidified and provides a substantially constant temperature product discharge. The system also obviates the problem of unbalancing of the refrigerating system following a defrosting cycle of operation. The system also provides a two stage refrigeration system which is capable of manual or automatic control with minimal switching valves and piping. The system provides flash type accumulators in combination with flooded evaporators (heat exchangers) which insure relatively constant product outlet temperature by assisting in compensating for any sudden surges in pressure above the desired system temperature-pressure. The system provides optimum oil separation and removal by effecting oil separation and removal at a point where the oil is relatively viscose and at a pressure above atmospheric pressure so that it can be removed without pumping.

Although but one embodiment has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes can be made in the arrangement of parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

I claim:

1. The process for separating one fluid in suspension in another fluid by reducing the temperature in a heat eX- change means sufficiently to cause the one fluid to solidify and thereby separate from the other fluid comprising the steps of passing the fluids in indirect heat exchange relationship with refrigerating fluid in a first heat exchanger to reduce the temperature to cause the one fluid to solidify and thereby separate from the other fluid by adhering to the internal surfaces of the heat exchanger passing refrigcrating fluid into a second heat exchanger to reduce the temperature of the internal surfaces of the heat exchanger to a predetermined value, stopping flow of fluids through said first heat exchanger and directing further flow of fluids through the second heat exchanger when the amount of accumulated solidified fluid on the internal surfaces of the first heat exchanger approaches the point at which heat transfer eflicency of the latter is adversely affected, heating the first heat exchanger to a temperature suflicient to cause the solidified fluid to change to a fluid state and removing the same from the first heat exchanger, and thereafter flowing refrigerating fluid through said first heat exchanger to reduce the temperature thereof to a predetermined value before redirecting flow of fluids therethrough.

2. The process for separating moisture suspended in a product fluid by reducing the temperature in a heat exchange means sufliciently to cause the moisture to freeze and separate from the product fluid in the form of frost, comprising the steps of passing the product fluid in indirect heat exchange relationship With refrigerating fluid in a first heat exchanger to reduce the temperature to cause the moisture to freeze and adhere to the internal surfaces of the heat exchanger, passing refrigerating fluid into a second heat exchanger to reduce the temperature of the internal surfaces of the heat exchanger to a predetermined value, ceasing flow of product fluid through said first heat exchanger and directing further flow of product fluid through the second heat exchanger when the amount of accumulated frost approaches the point at which heat transfer er'liciency of the heat exchanger is adversely affected, heating the first heat exchanger to a temperature sufflcient to cause the melting of the frost and removing the water from the heat exchanger, and thereafter flowing refrigerating fluid through said first heat exchanger to reduce the temperature thereof to a predetermined value before redirecting flow of fluid therethrough.

3. The process of claim 2 wherein high pressure-high temperature gaseous refrigerating fluid is passed into the first and second heat exchangers to heat them and effect defrosting of the internal surfaces thereof.

4. The process of claim 2 wherein high pressure-high temperature gaseous refrigerating fluid is bled from the first and second heat exchangers to gradually reduce the fluid pressure in the first and second heat exchangers to the normal system pressure.

5. The process of claim 2 wherein flow of refrigerating fluid through the first heat exchanger to reduce the temperature thereof is controlled so as to maintain a substantially constant suction line pressure.

6. A system of separating fluids from a mixture of fluids by causing at least one of the fluids to solidify, the system comprising (a) a plural stage refrigerating system having a compressor means for each stage for providing refrigerant fluid at different pressure-temperature values,

(b) an accumulator for each of the stages of the plural stage refrigerating system connected to said compressor means of the associated stage to receive refrigerant fluid and provide a reservoir of refrigerant fluid,

(c) a plurality of heat exchangers for each of the stages,

(d) the heat exchangers of one stage being arranged with the heat exchangers of the other stages in sets With the heat exchangers of each set connected together for series flow of said fluid mixture therethrough,

(e) the heat exchangers of each set of heat exchangers being connected to an accumulator of each stage to receive refrigerant at successively lesser pressuretemperatures with respect to the direction of the fluid mixture flow through the serially connected heat exchangers,

(f) each of said heat exchangers being constructed and arranged with a means for internally passing the fluid mixture in indirect heat exchange relationship with refrigerant fluid,

(g) control means for providing fluid mixture flow through one set of series connected heat exchangers at a time and for preventing flow through the other sets of series connected heat exchangers,

(h) level control means connected to each of said accumulators to maintain a predetermined level of refrigerant fluid in each of said accumulators,

(i) means connecting the low pressure accumulator to the high pressure accumulator to receive liquid refrigerant from the latter in accordance With the demand on the associated stage of the low pressure accumulator, and

(j) heating means connected to each of said heat exchangers to convert the solidified fluid to a fluid state to enable the removal of the fluid from the heat exchangers.

References Cited UNITED STATES PATENTS 1,842,263 1/1932 Gobert 62-12 2,252,739 8/1941 Stoever 6212 2,534,274 12/1950 Kniel 62-40 X 3,076,318 2/1963 Becker.

3,138,007 6/1964 Friedman et al. 62-278 3,151,470 10/1964 Quick 62-278 3,212,276 10/1965 Eld et a1 62-40 X 3,261,167 7/7966 Carr 6212 NORMAN YUDKOFF, Primary Examiner. V. W. PRETKA, Assistant Examiner. 

